Soaring energy price and global warming have stimulated growing research interest in new energy technologies. Solar cells could provide clean and renewable energy that can reduce the world's dependence on fossil fuel. Currently, the dominant solar cell technology is based on solid-state semiconductor materials, including polycrystalline silicon, amorphous silicon, cadmium telluride (CdTe), and copper indium gallium diselenide Cu(In, Ga)Se2. These types of solar cells have high power conversion efficiency; however, suffer from high manufacture cost. Dye sensitized solar cells and polymer/inorganic semiconductor hybrid solar cells are promising alternatives as they offer advantages of low cost, simple processing and potential large-scale production.
In these devices, the photoexcitation takes places in the dye (polymer) molecules and photogenerated charges are separated at the dye/oxide (polymer/oxide) interface. As the light-harvesting dye (polymer) molecules are present as a thin layer, the surface area of the semiconductor oxide must be substantial in order to achieve efficient light absorption. The electron transport in the semiconductor oxide is dominated by diffusion; therefore, it is necessary to reduce the charge traps in the semiconductor oxides for fast electron transport. In these solar cells, a transparent conducting oxide (TCO) serves as an optical window, which determines the amount of light entering the device, and as the electrode, which extracts photocurrent. The reduction of TCO cost is very important for the commercialization of these solar cells.